Cooperative cam phaser and air throttle control

ABSTRACT

Methods and apparatus relate to air handling for an internal combustion engine system, particularly utilizing premixed air and fuel. The engine system includes an intake air throttle (IAT) having a position set in response to the engine speed and a variable valve timing module having an intake valve timing set in response to the engine load. The variable valve timing module may be a cam phaser having a position at or between full retard and full advance positions. The engine system may operate in a transient mode or a fuel efficiency mode. The IAT position is adjusted in response to an engine speed error value or set at full throttle. The cam phaser position is adjusted in response to a pressure difference across the IAT, the engine speed, or is set to a limit position.

TECHNICAL FIELD

This disclosure generally relates to the control of an internalcombustion engine system. More specifically, this disclosure relates tothe cooperative control of an intake valve timing and an air throttle inan internal combustion engine.

BACKGROUND

Internal combustion engine systems are often required to meet variousperformance goals, including engine speed, power production, efficiency,and regulatory requirements. For example, achieving a target enginespeed is important in utility power generation applications forsynchronization with the electrical grid. To achieve these performancegoals, it is often desirable to control the contents of an enginecylinder during combustion, including the amount of air and its relatedcharacteristics (e.g., temperature and pressure). Among the techniquesto control the airflow into one or more engine cylinders, internalcombustion engine systems often include an intake throttle and a cam.The intake throttle is often adjustable for providing a desired flow ofair from the ambient environment to an intake manifold. Air is deliveredfrom the intake manifold to an engine cylinder through an intake valve,the opening and closing of which may be controlled by the cam. The flowof air to the engine cylinder can be adjusted with the presence of a camphaser, which is one technique of variable valve control or timing, tochange the phase of the cam (e.g., timing of valve opening and closing,which affects the amount of air that flows into the engine cylinder) andthus to provide a desired amount of air to the engine cylinder. As theoperating conditions of the engine change, the desired amount of airflowmay change in order to reach the various performance goals required.

SUMMARY

Aspects of various embodiments relate to a method of air handling for anengine system during stoichiometric combustion. An engine speed and anengine load of the engine system are determined. The engine load is oneof an actual engine load and a predicted engine load. An intake airthrottle (IAT) position is set in response to the engine speed. Anintake valve timing is set in response to the engine load. Setting theintake valve timing may include setting at least one of a cam phaserposition and an intake valve open duration.

An engine operating mode for the engine system may be determined inresponse to the engine load, wherein the engine operating mode is one ofa transient mode and a fuel efficiency mode. A transient mode may bedetermined in response to a partial engine load, wherein the intakevalve timing is set to improve transient response time. In the transientmode, the IAT position may be set in response to an engine speed errorvalue and/or an engine load to maintain a target engine speed.

A fuel efficiency mode may be determined in response to a higher engineload than the partial engine load range. In the fuel efficiency mode,the IAT position may be set in response to an engine speed, the engineload, and/or the engine speed error value to maintain a target enginespeed. The intake valve timing may be set in response to the engineload, a pressure difference across the IAT, an effective compressionratio (ECR), and/or a pressure difference error value across the IAT.

In addition or alternatively, in a fuel efficiency mode, the IATposition may be set to a full throttle position, and the intake valvetiming may be set in response to the engine speed and/or an engine speederror value to maintain a target engine speed.

Some embodiments relate to an engine controller comprising a hardwaredescription module (HDM), an air handling determination module (AHDM),and a hardware command module (HCM). The HDM provides one or more engineparameters, including an engine speed and an engine load. The engineload is one of an actual engine load and a predicted engine load. TheAHDM provides an IAT position in response to the engine speed andprovides an intake valve timing value in response to the engine load.The HCM provides an IAT command in response to the IAT position and anintake valve timing command in response to the intake valve timingvalue.

Further embodiments relate to an engine system comprising an airhandling system and an engine block. The air handling system includes anintake air path, an IAT along the intake path having an IAT position,and a cam phaser along the intake path having a cam phaser position. Theengine block includes a set of cylinders in fluid communication with theintake air path. The engine system further comprises means forcontrolling the IAT position and the cam phaser position to improvetransient response time in a transient mode and to improve brake thermalefficiency in a fuel efficiency mode.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an engine system including aprocessing subsystem, according to some embodiments.

FIG. 2 is a schematic illustration showing the processing subsystem ofFIG. 1 including a controller, according to some embodiments.

FIG. 3 is a flowchart diagram of an example procedure of operating anengine system, according to some embodiments.

FIG. 4 is a flowchart diagram of an example procedure for operating anengine system in a transient mode, according to some embodiments.

FIG. 5 is a flowchart diagram of example procedure for operating anengine system in a fuel efficiency mode, according to some embodiments.

FIG. 6 is a flowchart diagram of an example procedure for operating anengine system in another fuel efficiency mode, according to someembodiments.

FIGS. 7, 8, and 9 are illustrations of example plots and showing theposition of an IAT and a cam phaser during operation of an enginesystem, according to some embodiments.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof and in which are shown,by way of illustration, specific embodiments in which the invention maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

FIG. 1 is a schematic illustration of an engine system 10, according tosome embodiments. As shown, the engine system 10 is configured tooperate with premixed air and fuel, such that engine torque iscontrolled by the mixed air flow. Fuels that may be used with a premixedair and fuel configuration are, for example, natural gas or gasoline. Insome embodiments, the engine runs at stoichiometric combustion so thatthe ratio between air and fuel is stoichiometric (e.g., in aspark-ignition engine utilizing natural gas). In various embodiments,the engine system 10 runs at a non-stoichiometric ratio for combustion(e.g., lean burn).

As illustrated, the engine system 10 includes an engine 12 having anexternal load 14 coupled to the crankshaft of the engine 12 to apply aload thereto. In some embodiments, the external load 14 is an electricalgenerator, for example, which may provide power to an electrical grid.In additional embodiments, the external load 14 may be a compressor or atransmission (e.g., in a vehicle application).

Some applications for the engine system 10 will involve applying anexternal load 14 to the crankshaft of a warmed-up engine system 10.Typically, the load applied at first is a fraction of the rated load, ora partial load. Then, the applied load is increased by the external load14 over time (e.g., on the order of seconds or minutes) until the ratedload is applied. Such increases may be continuous or discrete. Thisphase of operation may be referred to as “load pickup.” The enginesystem 10 is advantageously configured to improve transient responsetime, or quickly transition from a lower load to a higher load, duringload pickup by operating in a transient mode. Once a high load or therated load is applied, the engine system 10 often does not need tochange engine load quickly (e.g., steady state) and is operating near anominal engine speed and near a rated engine load. During nominaloperation, the engine system 10 is advantageously configured to improvebrake thermal efficiency in a fuel efficiency engine operating mode,which allows the engine system to run at relatively lower cost than thetransient mode in terms of fuel consumption. The details of the enginesystem 10 and its operation are described herein in more detail.

In the illustrated embodiment, the example engine system 10 includes anair handling system 16 for providing charge air to the engine 12, afueling system 18 for providing fuel to the air handling system 16and/or the engine 12, and an exhaust system 20 for venting exhaust fromcombustion away from the engine 12. As used throughout this disclosure“charge air” may refer to ambient air, exhaust gas recirculated air,fuel-charged air, or any related variations or combinations thereof.

The example engine 12 includes cylinders 22 for combusting the chargeair to provide power for rotating the crankshaft. Generally, thecylinders 22 have a geometric compression ratio that is fixed,particularly during operation of the engine system 10. The geometriccompression ratio is the ratio of in-cylinder volume between top deadcenter (TDC) and bottom dead center (BDC).

Air is delivered to each of the cylinders 22 by the air handling system16 along an intake air path. In some embodiments, the air handlingsystem 16, includes an intake air line 24 including an intake 26, oftenwith an air cleaner, for receiving a flow of charge air from the ambientenvironment, an intake air throttle (IAT) 28 for regulating the flow ofcharge air along the intake air line, an intake manifold 30 to receivethe regulated flow of charge air from the intake air line, and a camdrive 32 for regulating the time that the intake valves are open anddelivering charge air to the cylinders 22 from the intake manifold.After charge air is combusted in the cylinders 22, exhaust leaves thecylinders through an exhaust path including, for example, an exhaustmanifold 34 and an exhaust line 36.

The engine system 10, as shown, further includes an optionalturbocharging system 38 coupled to the air handling system 16 and theexhaust system 20. As illustrated, the turbocharging system 38 includesa turbocharger having a compressor in fluid communication with theintake air line 24 to pressurize charge air upstream of the IAT 28 andincludes a turbine in fluid communication with the exhaust line 36downstream of the exhaust manifold 34. In some embodiments, theturbocharging system 38 includes multiple turbochargers to form amulti-stage turbocharging system (e.g., a two-stage turbocharging systemwith a high-stage stage and a low-stage). In some cases, theturbocharging system 38 is considered part of the air handling system 16for control purposes.

The example IAT 28 is positioned along the intake air line 24 upstreamof the intake manifold 30 to adjust the charge air flow to the intakemanifold. In some embodiments, the IAT 28 is a valve, such as abutterfly valve. The IAT 28 is adjustable through a range, for example,between a closed position (e.g., no throttle) and a wide open position(e.g., full throttle) by continuous and/or discrete amounts. For abutterfly valve, the fully open position corresponds to the valve beingparallel with the charge airflow through the intake air line 24. In someembodiments, the IAT 28 has a nominal position in response to an enginespeed and an engine load, which is determined during calibration andsometimes stored in one or more tables in memory (e.g., engine speed andengine load as inputs, IAT position as output).

In various embodiments, there is a pressure drop or pressure difference(e.g., delta pressure or ΔP) across the IAT 28. The wider or more openthe IAT 28 is, the lower the pressure differential is across the IAT.When the IAT 28 at full throttle, for example, the pressure differentialmay be equal to 0 psi or very low (e.g., 2 or 3 psi). Accordingly, themore closed the IAT 28, the higher the pressure differential is acrossthe IAT.

In some embodiments, the position of the IAT 28 is controlled bymechanical means. The example IAT 28 has a relatively fast response timefor the air handling system 16.

In the illustrated embodiment, the cam drive 32 includes a variablevalve module 40 to adjust the timing and/or duration that the intakevalves are open and/or closed in order to adjust the volumetricefficiency in the cylinders. As the cam lobes rotate, the intake valvesand optionally the exhaust valves are opened and closed.

The variable valve module 40 in the form of a cam phaser, for example,opens the valves earlier or later depending on its position. In someembodiments, the variable valve module 40 in the form of a cam phaserforms at least part of a variable valve timing (VVT) system. Althoughthe variable valve module 40 in the form of a cam phaser is discussedherein in more detail, this disclosure recognizes that a variable valveactuation (VVA) system may also be utilized. In other embodiments, thevariable valve module 40 is capable of independently shortening orextending the duration the intake valves are open as part of a VVAsystem.

In some embodiments, the variable valve module 40, which is herein alsoreferred to as cam phaser 40 as a non-limiting example of a variablevalve module, is adjustable through a range, for example, between afully advanced position and a fully retarded position by continuousand/or discrete amounts. The cam phaser 40 may also have a nominalposition corresponding to the design of the engine 12, which is betweenan advance limit and a retard limit. A retard range of the cam phaser 40is between the retard limit and the nominal position. An advance rangeof the cam phaser 40 is between the advance limit and the nominalposition. In some embodiments, the nominal position of the cam phaser 40is determined during calibration and sometimes stored in one or moretables in memory (e.g., engine speed and engine load as inputs, camphaser position as output).

Each position of the cam phaser 40 corresponds to a phase (e.g., timing)that the intake valves are open relative to the crankshaft position orpiston position during a combustion cycle. For example, during theintake stroke in a four-stroke combustion cycle (e.g., intake to BDC,compression to TDC, power to BDC, and exhaust to TDC), a nominalposition of the cam phaser 40 may correspond to the intake valvesopening at TDC (e.g., the beginning of the intake stroke) and closing atBDC (e.g., the end of the intake stroke).

With the nominal position defined in this way, a cam position in theretard range would correspond to the intake valves opening later, suchas after TDC (e.g., during the intake stroke) and closing later, such asafter BDC (e.g., during the compression stroke). The corresponding fullretard position of the cam phaser 40 would open the intake valves at alatest time allowed by the cam phaser (e.g., 20 degrees) during theintake stroke and close the intake valves at a latest time allowed bythe cam phaser (e.g., 20 degrees) during the compression stroke tomaximize the filling of the engine cylinders from the pressurized intakemanifold.

Accordingly, a cam position in the advance range would correspond to theintake valves opening earlier, such as before TDC (e.g., during theexhaust stroke) and closing easlier, such as before BDC (e.g., duringthe intake stroke). The corresponding full advance position of the camphaser 40 would open the intake valves at an earliest time allowed bythe cam phaser (e.g., 20 degrees) during the exhaust stroke prior to TDCand close at an earliest time allowed by the cam phaser (e.g., 20degrees) during the intake stroke prior to BDC to minimize the fillingof the engine cylinders from the pressurized intake manifold.

In some embodiments, the cam phaser 40 is a gear with an inner portionand an outer portion and is hydraulically adjustable throughout itsrange. The example cam phaser 40 has a relatively slower response timecompared to the response time of the IAT 28. In other embodiments, forexample, a VVA system includes a lost motion system, and a longestduration that the valves are open corresponds to the “full retard”position and a shortest duration that the valves are open corresponds tothe “full advance” position of the VVT system.

As shown, the engine system 10 includes a controller 42 operativelycoupled to one or more other components of the engine system, whichperforms certain operations to measure parameters and to control the oneor more components. Although the controller 42 may be coupled to severalcomponents, operative coupling of the controller 42 with the IAT 28 andthe cam phaser 40 is shown. The example controller 42 provides one ormore commands to adjust characteristics of charge air flow to thecylinders 22.

As illustrated, the controller 42 is coupled to one or more sensors,which may be along the intake air path, the exhaust path, or elsewherein the engine system 10. Example sensors, as shown, include an IATpressure sensor 44, a compressor outlet pressure sensor 46, an intakemanifold pressure (IMP) sensor 48, an exhaust manifold pressure (EMP)sensor 50, a turbine inlet pressure sensor 52, an engine speed sensor54, and a mass flow sensor 56 (e.g., at intake or exhaust). However, oneor more of these sensors may be excluded in various embodiments of theengine system 10.

The example IAT pressure sensor 44 is a differential pressure sensorproviding a relative pressure difference between the charge air flowupstream and downstream of the IAT 28. In other embodiments (not shown),the IAT pressure sensor 44 comprises an upstream absolute pressuresensor and a downstream absolute pressure sensor, and the controller 42interprets the absolute pressure sensor values to provide a pressuredifference. The example compressor outlet pressure sensor 46 and turbineinlet pressure sensor 52 are shown positioned relative to a singleturbocharger. In alternative embodiments (not shown) having twoturbochargers, the sensors 46, 52 may be placed relative to thehigh-pressure turbocharger, the low-pressure turbocharger, or a mixthereof. The example mass flow sensor 56 is positioned to measure thecharge air flow along the intake air path.

In some embodiments, the controller 42 may be considered to include anyof these sensors, in addition to other sensors. While in otherembodiments, the controller 42 may exclude one or more of these sensors.

Many aspects of this disclosure are described in terms of sequences ofactions to be performed by elements of a driver, controller, moduleand/or a computer system or other hardware capable of executingprogrammed instructions. These elements can be embodied in a controllerof an engine system, such as an engine control module or unit (ECM orECU), or in a controller separate from, and communicating with anECM/ECU. In an embodiment, the controller and/or ECM/ECU can be part ofa controller area network (CAN) in which the controller, sensor, and/oractuators communicate via digital CAN messages. It will be recognizedthat in each of the embodiments, the various actions for implementingthe control strategy could be performed by specialized circuits (e.g.,discrete logic gates interconnected to perform a specialized function),by program instructions, such as program modules, being executed by oneor more processors (e.g., a central processing unit (CPU) ormicroprocessor), or by a combination of both, all of which can beimplemented in a hardware and/or non-transient computer readableinstructions of the ECM/ECU and/or other controller or pluralcontrollers. Logic of embodiments consistent with the disclosure can beimplemented with any type of appropriate hardware and/or non-transientcomputer readable instructions, with portions residing in the form ofcomputer readable storage medium with a control algorithm recordedthereon such as the executable logic and instructions disclosed herein,and can be programmed, for example, to include one or more singular ormultidimensional lookup tables and/or calibration parameters. Thecomputer readable medium can comprise a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), an optical fiber, and a portable compact discread-only memory (CD-ROM), or any other solid-state, magnetic, and/oroptical disk medium capable of storing information. Thus, variousaspects can be embodied in many different forms, and all such forms arecontemplated to be consistent with this disclosure.

In some applications, when a load is applied, the engine system 10 istasked with “pushing” against the applied load to provide power at aconstant or target engine speed. A certain amount of charge air isrequired for combustion to maintain the engine speed while “pushing”against the applied load. The example engine system 10 makes beneficialuse of both the IAT 28 and the cam phaser 40 to adjust the amount ofcharge air delivered into the cylinders 22. In particular, the exampleengine system 10 sets an IAT position and a cam phaser position inresponse to the engine speed and/or the engine load with command(s) fromthe controller 42. For some cases, the IAT position and/or cam phaserposition are set further in response to a target engine speed and atarget engine load.

Engine load may be an actual engine load or a predicted engine load.Actual engine load is determined in response to one or more sensormeasurements. For example, the actual engine load may be determined inresponse to one or more measurements from the compressor outlet pressuresensor 46, the IMP sensor 48, the EMP sensor 50, the turbine inletpressure sensor 52, and the mass flow sensor 56. However, one or more ofthese measurements may also be excluded. In some embodiments, the actualengine load is determined in response to an EMP measurement. In variousembodiments, the actual engine load is determined in response to a loadsignal. For example, a load signal may be a kilowatt load signalprovided by a generator tasked with being the external load 14.

Accordingly, a predicted engine load relates to an engine load in aforward-looking time horizon. In some embodiments, the predicted engineload includes a predicted torque demand (e.g., reactive) or a desiredengine load (e.g., proactive) a few seconds into the future based on oneor more engine parameters.

In some embodiments, the example engine system 10 sets an IAT positionin response to the engine speed and sets a cam phaser position inresponse to the engine load with command(s) from the controller 42. TheIAT 28 is a faster controller than the cam phaser 40 and is suitable forquickly controlling the engine speed. In some applications, such aselectrical generation for a power grid, synchronization of the enginespeed with the power grid and thus maintaining a precise engine speed isan important requirement.

On the other hand, the cam phaser 40 is suitable for directlycontrolling the effective compression ratio (ECR) of the engine 12 orvolumetric efficiency. ECR is defined as an intermediate variable, whichis calculated from at least EMP and IMP and gives heavier weighting tothe EMP. Thus, the ECR is less affected by the position of the IAT 28than the position of the cam phaser 40.

Furthermore, the cam phaser 40 is optionally adjusted in response to atarget pressure differential across the IAT 28. For example, once an IAT28 position is set, this establishes a pressure differential across theIAT 28, and by setting the cam phaser 40 into a retarded position (e.g.,more air to the cylinders), the IAT pressure differential will increasedue to reduced pressure in the intake manifold. Similarly, by settingthe cam phaser 40 into an advanced position (e.g., less air to thecylinders), the IAT pressure differential will decrease due to elevatedpressure in the intake manifold. In general, the higher the pressuredifferential, the lower the open cycle efficiency of the engine system10 (e.g. higher pumping loss), and vice versa. On the other hand, thehigher the pressure differential, the greater influence the position ofthe IAT 28 will have on the charge air flow to the cylinders. With thisrecognition, the cam phaser 40 can be adjusted in cooperation with theIAT 28 to maintain a pressure differential to balance open cycleefficiency and/or pumping loss, and thus brake thermal efficiency, withcontrol of the charge air to the cylinders by the IAT.

In addition, the example engine system 10 changes control mode inresponse to the operating condition of the engine system 10. Forexample, the engine system 10 may recognize a partial load conditionwhen the target engine load is in a partial load range, which may rangefrom 0% to less than 100% of the rated load. Non-limiting examples ofpartial load ranges include 0% to 50%, 20% to 60%, or 0% to 80%. Invarious embodiments, the partial load range is a range less than athreshold load, such as 50% of the rated load.

In response to the partial load, which may mean the target engine loadis changing every few seconds or minutes, the example engine system 10enters into a transient mode and sets the cam phaser 40 into a fullretard position to improve volumetric efficiency and/or ECR, and thusimproves the transient response time by allowing the greatest amount ofair to be delivered into the cylinders 22 at each engine speed. In someembodiments, the IAT 28 is set into an initial position in response tothe target engine speed to control the engine speed with the IAT'srelatively quick response time. In various embodiments, the IAT 28position is further set or adjusted into a feedback position, which isdetermined in response to comparing the engine speed with the targetengine speed (e.g., an engine speed error value).

As used herein, the term “error value” means the result determined inresponse to the comparison of two values or sets of values. For example,an error value may be the difference between an actual/measured valueand a target value. Other types of error calculations and comparisonsknown to those having skill in the art are also contemplated.

In another example, the engine system 10 may recognize or interpret ahigh load condition greater than the partial load range up to 100% ofthe rated load. In response to the high load condition, which may meanthe target engine load is changing less rapidly, the example enginesystem 10 enters into a fuel efficiency mode and sets the IAT 28 into aninitial position in response to the target engine speed and the targetengine load to control the engine speed. In various embodiments, andsimilar to transient mode operation, the IAT 28 position is further setor adjusted into a feedback position, which is determined in response tocomparing the engine speed with the target engine speed (e.g., an enginespeed error value).

Also, in response to the high load condition, the example engine system10 also sets the cam phaser 40 into an initial position in response toat least one of a target engine load, a target pressure differenceacross the IAT, and/or a target ECR. In various embodiments, the camphaser 40 is further set or adjusted in response to a comparing theactual pressure difference across the IAT 28 to the target pressuredifference (e.g., pressure difference error value). In some embodiments,the initial position and the feedback position of the cam phaser 40 areadvanced relative to a nominal position of the cam phaser.

In a further or alternative embodiment, in response to the high loadcondition, the engine system 10 enters into an alternative fuelefficiency mode. In the alternative fuel efficiency mode, the IAT 28 isset into a full throttle position and the cam phaser 40 is set into aninitial position in response to the target engine speed. Furthermore,the cam phaser 40 may be set into a feedback position in response to anengine speed error value.

In certain embodiments, the controller 42 forms a portion of aprocessing subsystem 200 (FIG. 2) including one or more computingdevices having memory, processing, and communication hardware. Thecontroller 42 and its functionality may be implemented in any knownmanner. For example, the controller 42 may be a single device or adistributed device, and the functions of the controller may be performedby hardware and/or as computer instructions on a non-transient computerreadable storage medium.

In certain embodiments, the controller 42 includes one or more modulesthat functionally execute the operations of the controller. Thedescription herein includes modules emphasizes the structuralindependence of certain aspects of the controller 42, and illustratesone grouping of operations and responsibilities of the controller. Othergroupings that execute similar overall operations are understood withinthe scope of this disclosure. Modules may be implemented in hardwareand/or as computer instructions on a non-transient computer readablestorage medium, and modules may be distributed across various hardwareor computer based components.

Example and non-limiting module implementation elements include sensorsproviding any value determined herein, sensors providing any value thatis a precursor to a value determined herein, datalink and/or networkhardware including communication chips, oscillating crystals,communication links, cables, twisted pair wiring, coaxial wiring,shielded wiring, transmitters, receivers, and/or transceivers, logiccircuits, hard-wired logic circuits, reconfigurable logic circuits in aparticular non-transient state configured according to the modulespecification, any actuator including at least an electrical, hydraulic,or pneumatic actuator, a solenoid, an op-amp, analog control elements(springs, filters, integrators, adders, dividers, gain elements), and/ordigital control elements.

FIG. 2 is a schematic illustration showing the processing subsystem 200including controller 42, according to some embodiments. The exampleprocessing subsystem 200 includes one or more inputs 205 for providingindications to the example controller 42 and one or more outputs 210 forproviding commands from the example controller 42. The input(s) 205 andoutput(s) 210 are not limited in any particular manner and may be, forexample, of a mechanical, electrical, electronic, electromagnetic,and/or optical nature. The one or more inputs 205 may include, forexample, an indication from one or more of the sensors 44, 46, 48, 50,52, 54, and 56 (FIG. 1) as applicable. The one or more outputs 210 mayinclude, for example, a command to the IAT 28 and/or the cam phaser 40,as applicable.

As further illustrated, the controller 42 includes a hardware definitionmodule (HDM) 215, an air handling determination module (AHDM) 220, and ahardware command module (HCM) 225. The example controller 42 alsoincludes one or more parameters related to the engine system, such as anengine speed 230, an engine load 235, a target engine speed 240, anengine speed error value 245, an engine operating mode 250, an IATposition 255, an intake valve timing value 257, a cam phaser position260, an intake valve open duration 262, a pressure difference across theIAT 265, a target pressure difference across the IAT 270, a pressuredifference error value 275 (e.g., across the IAT), and/or a target ECR280.

The example HDM 215 interprets or determines one or more parametersavailable to the controller 42 for storage, output, and/or furtherprocessing by modules in the controller. For example, the HDM 215 mayinterpret or determine one or more of the engine speed 230, the engineload 235, the target engine speed 240, the engine speed error value 245,the pressure difference across the IAT 265, the target pressuredifference across the IAT 270, the pressure difference error value 275,and/or the target ECR 280. The example HDM 215 interprets parameters inresponse to input(s) 205 and/or other parameters available to thecontroller 42. In one example, the HDM 215 interprets the engine load235 as an actual engine load in response to input 205 from the EMPsensor 50. In another example, the HDM 215 interprets the engine speederror value 245 in response to a comparison of the engine speed 230(e.g., from the input 205 from the engine speed sensor 54) and thetarget engine speed 240 (e.g., a received, stored, or determined value).In some embodiments, to perform the functions described hereinthroughout, the HDM 215 may include one or more of an analog to digitalconverter (ADC), a processor, a non-transient computer readable storagemedium, a bus, wired/wireless connection hardware, and/or one or more ofthe sensors 44, 46, 48, 50, 52, 54, and 56 (FIG. 1). In otherembodiments, one or more of these may be excluded from the HDM 215.

The example AHDM 220 determines one or more parameters for control ofthe air handling system 16 (FIG. 1), such as the IAT position 255 andthe intake valve timing value 257. In some embodiments, the intake valvetiming value 257 includes a cam phaser position 260 (e.g., in a VVTsystem). In various embodiments, the intake valve timing value 257includes an intake valve open duration 262 (e.g., in a VVA system).These air handling control parameters are determined in response to oneor more engine parameters available to the controller 42. For example,the IAT position 255 and/or the intake valve timing value 257 may bedetermined in response to the engine speed 230 and/or the engine load235. In a further example, the IAT position 255 may be determined inresponse to the target engine speed 240 and/or the engine speed errorvalue 245. In yet another example, the intake valve timing value 257 maybe determined in response to the target engine speed 240, the enginespeed error value 245, the target pressure difference across the IAT270, the pressure difference error value 275, and/or the target ECR 280.In some embodiments, to perform the functions described hereinthroughout, the AHDM 220 may include one or more of a processor, anon-transient computer readable storage medium, a bus, and/orwired/wireless connection hardware. In other embodiments, one or more ofthese may be excluded from the AHDM 220.

The example HCM 225 provides one or more commands for component(s) ofthe engine system 10 in response to one or more control signals, such asan IAT position command and an intake valve timing command (e.g., camphaser position command). In some embodiments, to perform the functionsdescribed herein throughout, the HCM 225 may include, but is not limitedto, the IAT 28, the cam phaser 40, a processor, a non-transient computerreadable storage medium, a bus, and/or wired/wireless connectionhardware. In other embodiments, one or more of these may be excludedfrom the HCM 225.

FIG. 3 is a flowchart diagram of an example procedure 300 of operatingan engine system, such as engine system 10, according to someembodiments. In operation 305, an internal combustion engine is startedand warmed-up to a target engine speed (e.g., an idle engine speed). Thetarget engine speed may be fixed in some applications, such as forstationary power generation. The internal combustion engine may setup torun at stoichiometric combustion (e.g., for a natural gas engine).

In operation 310, an external load is applied to the internal combustionengine. The external load may be a generator, for example, in a powergeneration application that produces electrical power. Some externalloads are capable of varying the load applied to the internal combustionengine in a range from 0% to 100% of the rated load of the enginesystem, such as from 20% to about 100%.

In operation 315, an engine speed and an engine load of the enginesystem are determined. The engine speed may be determined in response toa measurement from an engine speed sensor. The engine load may be anactual engine load or a predicted engine load, such as a predictedtorque demand or a desired engine load.

In operation 320, an engine operating mode is determined in response tothe engine load. In the illustrated embodiment, the engine load may beclassified or categorized as a partial load or a high load. The partialload condition may be defined by a range or a threshold. The high loadcondition may be defined by a range or a threshold above the partialload range and may include the rated load of the engine system. Thedetermined engine operating mode may be a transient mode and/or a fuelefficiency mode.

Operation 325 is performed when a transient engine operating mode isdetermined in response to a partial load condition. In operation 325,the engine system is operated in a transient mode. In a power generationapplication, a partial load condition may indicate that the engine loadwill be increasing every few seconds toward a higher engine load, suchas the rated engine load. The engine system may benefit from a highervolumetric efficiency for a faster load pickup. An example procedure 400for carrying out operation 325 is shown in more detail in FIG. 4.

Operation 330 is performed when a fuel efficiency engine operating modeis determined in response to a high load condition. In operation 330,the engine system is operated in a fuel efficiency mode. In a powergeneration application, a high load condition may indicate that theengine load will not be changing quickly and/or that the engine systemis near a nominal or steady state operating condition. The engine systemmay benefit from a higher open cycle efficiency and lower pumping loss.Example procedures 500, 600 for carrying out operation 330 are shown inmore detail in FIGS. 5 and 6.

FIG. 4 is a flowchart diagram of an example procedure 400 for operatingan engine system in a transient mode, according to some embodiments. Inoperation 405, the cam phaser is set into a full retard position. Invarious embodiments, the full retard position corresponds to the highestECR position and/or a highest volumetric efficiency position for the camphaser.

In operation 410, the IAT is placed into an initial position (e.g., baseposition) in response to the engine speed and optionally the engineload. The initial position of the IAT, in conjunction with the fullyretarded cam phaser position, sets the amount of charge air flow beingdelivered to the cylinders, and thus controls the engine speed. In someembodiments, the initial IAT position is less open than a nominal IATposition. In various embodiments, the charge air flow corresponding tothe initial IAT position and the fully retarded cam phaser position isabout equal to the charge air flow corresponding to the nominal IATposition and the nominal cam phaser position. Operation 410 may beconsidered a feed-forward control operation.

In the illustrated embodiment, the procedure 400 proceeds into afeedback control operation or control loop after the engine speed and/orengine load have stabilized, in which each iteration measures enginespeed and sets the IAT position to a feedback IAT position. In operation415, the engine speed is measured. In operation 420, the engine speed iscompared with the target engine speed, which may be fixed for a powergeneration application. An engine speed error value may be determined inresponse to the comparison. In operation 425, the IAT position is set oradjusted in response to the comparison or the error value to maintainthe target engine speed.

In some embodiments, a feedback IAT position is determined in responseto the engine speed error value to reduce the error and maintain theengine speed in response to engine load disturbances. For example, whenthe applied engine load increases during load pickup, the engine speedis temporarily slowed below the target engine speed. Because enginespeed is monitored, in response to a slowed engine speed, the IATposition is adjusted to a more open position to increase the charge airflow, which returns the engine speed to the target engine speed. Thisfeedback control loop may continue to iterate until the engine system isoperated in another mode. In this manner, procedure 400 facilitatesresponding to increasing applied load while improving volumetricefficiency and/or ECR.

FIG. 5 is a flowchart diagram of an example procedure 500 for operatingan engine system in a fuel efficiency mode, according to someembodiments. As illustrated, the procedure 500 includes two controlpaths. The first control path begins with operation 505, in which thecam phaser is set into an initial position (e.g., base position) inresponse to the engine load. In various embodiments, the initial camphaser position is set to an advanced position in the advanced range inresponse to an engine load at or above 50%. In alternative embodiments,the initial cam phaser position is set to an advanced position inresponse to an engine load at or above 80%, or at an engine load between50% and 80%. In some embodiments, the initial cam phaser position isfully advanced at an engine load of about 100%.

The initial cam phaser position may be set further in response to theengine speed for some applications, for example, in which the targetengine speed is not fixed. Operation 505 may be considered afeed-forward control operation.

In various embodiments, the first control path for example procedure 500proceeds into a feedback control operation or control loop after theengine speed and/or engine load have stabilized, in which each iterationmeasures a pressure difference and sets the cam phaser position to afeedback cam phaser position. In operation 510, the pressure differenceacross the IAT is measured. In operation 515, the pressure differenceacross the IAT is compared with a target pressure difference across theIAT. A pressure difference error value may be determined in response tothe comparison. In operation 520, the cam phaser position is set oradjusted in response to the comparison or the error value to maintainthe target pressure difference across the IAT.

In some embodiments, the target pressure difference across the IAT isselected to provide a balance between a desired amount of control overcharge air flow and/or to reduce pumping loss. For example, as the IATposition becomes more wide open in response to higher engine speed, thepressure difference across the IAT temporarily decreases. Because thepressure difference is monitored to reduce the pressure difference errorvalue, the current cam phaser position is adjusted to a more retardedposition to decrease the pressure downstream of the IAT, which returnsthe pressure difference to the target pressure difference. This feedbackcontrol loop in the first control path may continue to iterate until theengine system is operated in another mode. Because the first controlpath involves setting the cam phaser, which is a slower actuator thanthe IAT, this control loop may be referred to as the “slow controlloop.”

The second control path for example procedure 500 begins with operation525, in which the IAT position is set to an initial position (e.g., baseposition) in response to the engine speed and optionally the engineload. In some embodiments, the IAT position is set more open than anominal IAT position. In various embodiments, the charge air flowcorresponding to the initial IAT position and the initial cam phaserposition (which is set in response to the engine load in operation 505)is about equal to the charge air flow corresponding to the nominal IATposition and the nominal cam phaser position. Operation 525 may beconsidered a feed-forward control operation.

In various embodiments, the second control path proceeds into a feedbackcontrol operation or control loop after the engine speed and/or engineload have stabilized, in which each iteration measures an engine speedand sets the IAT position to a feedback IAT position. In operation 530,the engine speed is measured. In operation 535, the engine speed iscompared with a target engine speed. An engine speed error value may bedetermined in response to the comparison. In operation 540, the IATposition is set or adjusted in response to the comparison or the errorvalue to maintain the target engine speed.

In some cases, maintaining the engine speed at the target engine speedis an important requirement. Because the IAT is a faster actuator thanthe cam phaser, the IAT position is suited for quickly reacting todisturbances in engine speed and adjusting the charge air flow. Aspreviously mentioned, the ability for the IAT position to influencecharge air flow is also influenced by the pressure difference across theIAT, which is set in the first control path by the cam phaser (operation520). Because the second control path involves setting the IAT, thiscontrol loop may be referred to as the “fast control loop.”

In this manner, the first and second control paths of procedure 500facilitates quickly responding to engine speed disturbances whilereducing pumping loss to improve open cycle efficiency, and thus brakethermal efficiency.

FIG. 6 is a flowchart diagram of an example procedure 600 for operatingan engine system in a fuel efficiency mode, according to someembodiments. Example procedure 600 may be a subprocedure of procedure500 or an alternative procedure replacing procedure 500. For example,procedure 600 may be utilized in procedure 500 only when the IAT is atfull throttle.

In operation 605, the IAT is set to a full throttle position. The fullthrottle positon corresponds to the lowest pressure difference acrossthe IAT, and the full throttle position also corresponds to a highestcharge air flow position, a highest open cycle efficiency position, alowest pumping loss position, and a highest brake thermal efficiencyposition for the IAT. In some embodiments, IAT may additionally oralternatively be set in response to the engine speed being at or nearthe target engine speed.

In operation 610, the cam phaser is set into an initial position (e.g.,base position) in response to the engine speed and optionally the engineload. The initial position of the cam phaser, in conjunction with thefully open IAT, sets the amount of charge air flow being delivered tothe cylinders, and thus controls the engine speed. Operation 610 may beconsidered a feed-forward control operation.

In various embodiments, the procedure 600 proceeds into a feedbackcontrol operation or control loop after the engine speed and/or engineload has stabilized, in which each iteration measures engine speed andsets the cam phaser position to a feedback cam phaser position. Inoperation 615, the engine speed is measured. In operation 620, theengine speed is compared with the target engine speed, which may befixed for a power generation application. An engine speed error valuemay be determined in response to the comparison. In operation 625, thecam phaser position is set or adjusted in response to the comparison orerror value to maintain the target engine speed.

In some embodiments, the cam phaser position is determined in responseto the engine speed error value to reduce the error and maintain theengine speed in response to engine load disturbances. For example, in aresponse to a temporarily reduced load (e.g., from 100% to 90%), theengine speed may increase above the target engine speed. Because enginespeed is monitored, in response to the faster engine speed, the camphaser position is adjusted to a more advanced position to reduce thecharge air flow, which returns the engine speed to the target enginespeed. This feedback control loop may iterate until the engine system isoperated in another mode. In this manner, procedure 600 facilitatesresponding to engine speed disturbances while improving open cycleefficiency, pumping loss, and/or brake thermal efficiency.

FIGS. 7, 8, and 9 are illustrations of example plots 700, 800, and 900showing the position of an IAT and a cam phaser during operation of anengine system, according to some embodiments. The example plots 700,800, 900 each include an engine load axis 710 (e.g., an X-axis), a camphaser position axis 720 (e.g., a first Y-axis), and an IAT positionaxis 730 (e.g., a second Y-axis).

Along the cam phaser position axis 720, an advance limit and a retardlimit are shown. In various embodiments, the advance limit correspondsto the earliest timing the intake valves open and close allowed by thecam phaser, while the retard limit corresponds to the latest timing theintake valves open and close allowed by the cam phaser. The nominal camphaser position is between the advance limit and the retard limit.

Along the IAT position axis 730, a full throttle position and a nothrottle position are shown. The full throttle position corresponds tothe lowest pressure difference across the IAT, while the no throttlelimit corresponds to the greatest pressure difference across the IAT.The nominal IAT position is between no throttle and full throttle.

Also shown is an example transient mode, which corresponds to an engineload range between 0% and 50% of the rated load of the engine system.FIGS. 7, 8 and 9 show the engine system operating in a transient modesimilar to example procedure 400 (FIG. 4). An example fuel efficiencymode corresponds to an engine load range above 50% of the rated load tothe rated load (e.g., 100%) of the engine system. FIG. 7 shows theengine system operating in a fuel efficiency mode similar to exampleprocedure 500 (FIG. 5). FIG. 8 shows the engine system operating in afuel efficiency mode similar to example procedure 600 (FIG. 6). That is,the engine system switches between transient mode and fuel efficiencymode at about 50% of rated load. FIG. 9 shows the engine systemoperating with gradual transitions between the transient mode and thefuel efficiency mode, according to either example procedure 500 (FIG. 5)or example procedure 600 (FIG. 6).

For illustrative purposes, the example plots 700, 800, and 900correspond to operating an engine system having a fixed target enginespeed. Furthermore, plots 700, 800, and 900 are illustrative only and donot represent actual test data.

In addition, for illustrative purposes, the example plots 700 and 800show sharp changes in IAT position and cam phaser position whentransitioning between modes to clearly show the change in behaviorbetween modes. In some embodiments, the IAT and cam phaser positions areadjusted gradually when transitioning between modes by changing therespective feedback target (e.g., without a setting an initial position)from the transitory mode target to the fuel efficiency mode target, forexample. An example of a gradual change is shown in example plot 900(FIG. 9).

As illustrated in FIG. 7, the example plot 700 shows the IAT position750 and the cam phaser position 760 as the engine load increases from 0%to 100% of the rated load. As shown, the IAT position 750 begins at aposition corresponding to an idle engine at 0% of rated load. As theload increases in the transient mode range from 0% to 50%, the IATposition 750 becomes more open to provide more charge air flow tomaintain the engine speed at increased load.

In the illustrated embodiment, in the transient mode range from 0% to50%, the cam phaser position 760 is at the full retard position.Accordingly, as shown, the IAT position 750 in the transient mode rangemay be less open than the nominal IAT position.

After the engine load surpasses 50% of rated load and enters into thefuel efficiency mode range, the cam phaser position 760 transitions tothe advanced range (e.g., more advanced than nominal) to open the intakevalves earlier and maintain a pressure difference across the IAT. In acooperative manner, the IAT position 750 also transitions to be moreopen to adjust for the lower volumetric efficiency due to the earlieropening and closing of the intake valves. As the engine load increasesin the fuel efficiency mode range, the cam phaser position 760 advancesand reaches the advance limit as the engine load approaches 100% ofrated load, in order to allow the IAT to be more open to reduce pumpinglosses due to the pressure difference across the IAT (e.g., improve opencycle efficiency) and to improve the influence of changes in the IATposition over the charge air flow. In the illustrated embodiment, theIAT position 750 increases with engine load but does not approach fullthrottle by design in order to give the IAT the ability to compensatefor load disturbances that would affect the engine speed. In thismanner, the IAT position 750 and the cam phaser position 760 cooperateto improve load pickup performance and maintain engine speed at highload, while improving brake thermal efficiency.

As illustrated in FIG. 8, the example plot 800 shows the IAT position850 and the cam phaser position 860. As shown, in the transient moderange, the IAT position 850 and cam phaser position 860 are similar toIAT position 750 and cam phaser position 760. After the engine loadpasses 50% of rated load and enters into a fuel efficiency mode range,however, the IAT position 850 transitions to a full throttle position inorder to minimize the pumping losses due to the pressure differenceacross the IAT (e.g., improve open cycle efficiency) and to increase thecharge air flow. In a cooperative manner, the cam phaser position 860transitions into an advanced range, which reduces the volumetricefficiency due to opening the intake valves earlier, which adjusts forthe greater charge air flow. As the engine load increases in the fuelefficiency mode range, the cam phaser position 860 retards toward thenominal position at 100% of rated load by design in order to give thecam phaser the ability to adjust the charge air flow in response to loaddisturbances that would affect the engine speed. In this manner, the IATposition 850 and the cam phaser position 860 cooperate to improve loadpickup performance and maintain engine speed at high load, whileimproving brake thermal efficiency.

As illustrated in FIG. 9, the example plot 900 shows the IAT position950 and the cam phaser position 960. As shown, in the transient moderange and the fuel efficiency mode range, the IAT position 950 increasesgradually toward full throttle. This gradual transition in the IATposition 950 corresponds to a similarly gradual increase in engine speedtoward the fixed, target engine speed for rated load operation. The camphaser position 960 remains at a full retard position through at least aportion of the transient mode range—as shown, from 0 to 30% of ratedload. From greater than 30% to 50% in the transient mode range, the camphaser position 960 advances gradually.

At about greater than 50% of rated load, in the fuel efficiency mode,the IAT position 950 continues to gradually increase toward fullthrottle. The transition between the transient mode and the fuelefficiency mode for the IAT position 950 is gradual. The cam phaserposition 960 continues to gradually increase for at least a portion ofthe fuel efficiency mode range, and also transitions gradually betweenmodes. The cam phaser position 960 reaches an advance limit prior torated load. As shown, the cam phaser position 960 reaches the advancelimit at about 70% of rated load and stays in the fully advancedposition from greater than 70% to 100% of rated load.

In the fuel efficiency mode, or once at rated load, the engine systemmay be operated at rated load according to either example procedure 500(FIG. 5) or example procedure 600 (FIG. 6), for example.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. For example, it is contemplated that featuresdescribed in association with one embodiment are optionally employed inaddition or as an alternative to features described in association withanother embodiment. The scope of the invention should, therefore, bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The following is claimed:
 1. A method of air handling for an enginesystem with premixed air and fuel upstream of at least one enginecylinder, comprising: determining an engine speed and an engine load ofthe engine system, wherein the engine load is one of an actual engineload and a predicted engine load; setting an intake air throttle (TAT)position in response to the engine speed; and setting an intake valvetiming in response to a pressure difference error value across the IATand the engine speed.
 2. The method of claim 1, further comprisingrunning the engine system with a fuel including at least one of naturalgas and gasoline, the fuel being premixed with air upstream of the atleast one engine cylinder at one of a stoichiometric or a lean burnratio.
 3. The method of claim 1, wherein setting the intake valve timingincludes setting at least one of a cam phaser position or an intakevalve open duration.
 4. The method of claim 1, wherein the IAT positionis set to a feedback IAT position in response to an engine speed errorvalue to maintain a target speed.
 5. The method of claim 1, furthercomprising receiving a load signal from an external load driven by theengine system and determining the engine load based on the load signal.6. The method of claim 5, wherein the external load comprises a powergenerator and the load signal is based on an electrical power of thepower generator.
 7. The method of claim 1, further comprisingdetermining an engine operating mode for the engine system in responseto the engine load, wherein the engine operating mode is one of atransient mode or a fuel efficiency mode.
 8. The method of claim 7,wherein the transient engine operating mode is determined in response toa partial engine load, and wherein the intake valve timing is set toimprove a transient response time.
 9. The method of claim 8, wherein theIAT position is set to an initial position in response to the enginespeed and the engine load.
 10. The method of claim 9, wherein the IATposition is set to a feedback position in response to an engine speederror value to maintain a target engine speed.
 11. The method of claim7, wherein the fuel efficiency mode is determined in response to ahigher engine load than a partial engine load range, wherein the IATposition is set to an initial IAT position in response to the enginespeed and the engine load.
 12. The method of claim 11, wherein theintake valve timing is set to an initial intake valve timing in responseto at least one of: the engine load, a pressure difference across theIAT, or an effective compression ratio (ECR).
 13. The method of claim11, wherein the initial IAT position is a full throttle position, theintake valve timing is set to an initial intake valve timing in responseto the engine speed; and the intake valve timing is set to a feedbackintake valve timing in response to an engine speed error value tomaintain a target speed.